1. Field of the Invention
This invention relates to photoreceptors for electrophotographic printing, and more particularly, this invention relates to a photoreceptor belt in combination with a cylindrical mandrel. Even more particularly, this invention relates to a photoreceptor belt removable attached to a lightweight cylindrical mandrel which is constructed of a machinable foam material.
The photoreceptor and cylindrical mandrel design of this invention is particularly well suited to replace the current belt or drum photoreceptor designs as presently used in electrophotographic printing machines. The present invention will help reduce various mechanical problems that are typically experienced in any electrophotographic apparatus that employs known combinations of a photoreceptor belt and cylindrical mandrel.
The photoreceptor and cylindrical mandrel design of this invention is particularly well suited for use in high speed production color printers, especially those printers that employ large drums which support the photoconductors. Large drums require large and heavy support structures for the drums.
2. Description of the Prior Art
In an electrophotographic mono-color printing machine an electrophotograpic process is employed in which a photoconductive member is charged to a substantially uniform potential. The charged portion of the photoconductive member is then exposed to a light reflected original document image. Exposure of the charged photoconductive member selectively dissipates the charge in the irradiated areas. This process records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing it into contact with toner. The toner image on the photoconductive member is subsequently transferred to a copy sheet. The copy sheet is then heated to permanently affix the toner image to the sheet. Multicolor electrophotographic printing is substantially identical, although more complex than the mono-color printing process. In a multicolor process, after the photoconductor is cleaned of residual toner, the copying process occurs again.
Cyclic and tandem color copying processes dominate the art of color printing. In a cyclic multicolor printing process, successive latent images corresponding to different colors are recorded on the photoconductive member during each cycle. Accordingly, one photoconductive member is required in this type of machine. The photoconductive member is used repetitively for each color/cycle. Each single color electrostatic latent image is developed with toner of a color complementary thereto. This process is repeated a plurality of cycles for the difference colors in an image and the respective complementary color tone. Each single color toner image is transferred to the copy sheet and superimposed with the prior toner image. This creates a multilayered toner image on the copy sheet. Thereafter, the multilayered toner image is permanently affixed to the copy sheet creating a color copy. The primary attributes of a cyclic printing machine are its relatively low number of parts and its low cost. U.S. Pat. No. 4,583,991, herein incorporated by reference, describes a cyclic printing machine in which a sheet moves in a recirculated path and successive color toner images are transferred thereto.
A typical tandem printing machine uses multiple printing engines to transfer, in one cycle, different colored tone images directly to a sheet or to an intermediate surface for subsequent transfer to the sheet. The fast printing rate is the primary advantage of a tandem machine since all colors are printed in one cycle. However, the complex equipment of a tandem machine leads to a higher total cost.
U.S. Pat. Nos. 4,796,050 and 4,803,518, herein incorporated by reference, disclose tandem printing machines having a plurality of photoconductive drums arranged such that color separated light images of an original document are recorded thereon as electrostatic latent images. The latent images are developed into visible color images. A conveyor advances a sheet past each photoconductive drum. Visible color images are transferred from each photoconductive drum to the sheet and then fixed to the sheet.
Both cyclic and tandem printing machines can use drum or belt type photoreceptors. Disadvantages are encountered in the use of photoconductive belts because especially high speed production color printers require multiple large photoreceptors. These large size photoreceptors can range in size from four inches to fifteen inches in diameter and up to twenty-seven inches long. The substrate (mandrels) which support these photoreceptor belts are usually formed of aluminum tubes that are very heavy and quite expensive to produce. An available alternative to this type of substrate is a thin metal or plastic cylinder which slips over a core cylinder i.e., a (Drelt). The core cylinder can either be a part of the machine or a part of the photoconductor. In any case, this core is also usually very heavy. In the case of the core being part of the machine, these heavy cylinders must be rotated, and continually started and stopped. Due to their large diameter, this creates mechanical problems due to the momentum and inertia properties of the heavy core. Additional horsepower is required to drive these cylinders, and additional braking and control mechanisms are required for stopping or changing speed of the photoreceptor. In the case where the core is a part of the photoconductor, the weight is also a concern since this assembly must be constantly handled by technical representatives, and also shipped to various locations.
Accordingly, it is a primary object of this invention to provide a new and improved mounting apparatus (mandrel) for a photoreceptor which avoids all of the disadvantages outlined above. The new and improved mounting apparatus for a photoreceptor in accordance with the features of this invention is made of a very lightweight material that can also be precision machined; has particular use when mounting a flexible belt photoreceptor on a rigid cylindrical base support, thereby forming a xe2x80x9cdreltxe2x80x9d photoreceptor for use in high speed production color printers; and provides a new and improved mandrel from which a photoreceptor can be easily removed and replaced. In addition to these advantages the present invention provides a mounting apparatus for a belt photoreceptor or a rigid thin walled cylinder which supports a photoconductive material, i.e. a drum.
To achieve the advantages in accordance with the purpose of the present invention, as embodied and broadly described herein, the photoreceptor apparatus of this invention comprises a cylindrical mandrel having a photoreceptor belt attached thereto. Attached as used herein means the photoreceptor belt is substantially fixed in a place on the full circumference of the mandrel at the longitudinal surface by preferably an interference fit or other known method. Preferably, the means for attaching the belt to the mandrel comprises a retractable segment mechanism that is isolated against the photoreceptor belt to hold the photoreceptor belt in place. Preferably, the photoreceptor belt is a multilayered continuous belt. The photoreceptor apparatus in accordance with the present invention comprises a photoreceptor belt in combination with a cylindrically shaped mandrel to which the photoreceptor belt is adapted to be mounted, the mandrel or support for the photoreceptor being made of a machinable foam material.
An electrophotographic imaging process in accordance with the features of the present invention comprises charging a photoconductive member to a substantially uniform potential, said photoconductive member comprising a photoreceptor belt attached to a cylindrically shaped mandrel, the mandrel comprising a machinable foam material; exposing the charged photoconductive member to a light reflective image to dissipate portions of the charge; transferring toner to the charge; and transferring the toner to a copy sheet.
The photoreceptor used with the present invention is utilizable as a replacement for previously known photoreceptor drums in printing machines, for example U.S. Pat. No. 5,121,171 herein incorporated by reference.
The photoreceptor belt in the current invention can be any type. U.S. Pat. No. 4,265,990, herein incorporated by reference describes various acceptable belt photoreceptors.